Method of returning gas to gasproducing formations



May 6, 1941.

n. R. CONLON, JR 2,240,550

METHOD OF RETURNING GAS T0 GAS-PRODUCING FORMATIONS Filed Dec. 15, 1939 Daniel 12. Canton, Jr. 1/ 7% 7 2; flitorney Patented May 6, 1941 UNITED STATES PATENT OFFICE- METHOD OF RETURNING GAS T GAS- w FRODUCING FOBMATIONS Daniel R. Gordon, In, Upper Darby, Pa, assignor 3 to The Atlantic Refining Company, Philadelphia, Pa", a corporation of Pennsylvania Application December 13, 1939, Serial No.309,'035

ducing formation.

7 Claims. (Cl. 166-21) The present invention relates to a method of turn as to gas and/or oil-producing formations, and more particularly to formations producing at relatively high pressures.

A principal object of this invention is a method of returning to ashigh pressure gas-producing formation, lean gas or gas which has been A further object of this invention is a method of returning gas to a. gas-producing formation associated with a. crude oil-producing formation, in order to repressure the formation or to maintain a pressure in the formation sufllcient to deliver crude oil to the earths surface without resort to expensive pumping operations.

A further object of this invention is a method of returning gas .to a high pressure gas-producing formation in such a manner that pressures substantially lower than the normal well head- .7 pressure may be employed in introducing the gas into the input well.

In the operation of high pressure wellsof the gas distillate type, wherein the gas produced by the well is subjected to treatment for the separation therefrom of liquid or liqueiiable hydrocarbons, it has been found desirable and in many oases mandatory, that the gas denuded of liqueturn the denuded gas to the producing forma tion, it is therefore necessary to recompress the gas to a pressure slightly above that existing at the well head, introduce the recompressed gas into the well, and conduct the gas downwardly through the well to the producing formation, against the gas pressure existing in said formation. For example, gas containing liquefiable hydrocarbons oi the nature of gasoline may be withdrawn from a gas distillate well producing at a well head pressure of the order 01' 3500 lbs./ sq. in. This gas may be stripped of its liquefiable hydrocarbon content-for example, by absorption at elevated pressure, and the stripped gas may be delivered to the return compressor at a pressure 0! about 3200-3300 lbs/sq. in. In order to return this gas to the producing formation through an adjacent input well, such gas is recompressed to a pressure at least as great as the well head pressure, and preferably somewhat in excess thereof, for example, 3600 lbs/sq. in., and is introduced into the input well against the pressure existing at the well head. By operating in this manner, it is necessary to employ com-.

pressors capable of continuously delivering the desired volume of stripped gas to the input well at relatively high pressure, 1. e., or the order of 3600 lbs/sq. in. Compressors or pumps suitable for high pressure operation are expensive both 'with respect to installation as well as maintenance.

However, in accordance with my invention, I am able to return gas to a high pressure formatlon without recourse to compressors or pumps capable of continuously delivering 89s to the input well at pressures greater than normal well head pressure. In other words, I am able to return gas .to the gas-producing formation at pump pressures substantially lower than those normally existing at the head of the input well.

Briefly, my invention comprises introducing gas and liquid, such as water, oil, or drilling mud, or the equivalent, into the input well, and conducting the gas and liquid downwardly through the well in such a manner that the liquid exerts which may be employed a hydrostatic pressure upon the gas sufllcient to overcome, at least in part, the gas pressure existingat the bottom oi. the well, i. e., the formation pressure. The gasis separated from the liquid adjacent the bottom 01' the well, and the liquid is forced to the earth's surface by the pressure existing in the well, the gas passing from the well into the formation. If desired, both the gas and the liquid may be passed from the well into the producing formation. By operating in this manner, a considerable portion of the formation pressure is overcome by the hydrostatic head of the liquid introduced with the gas, thus permitting the use of lower pump pressures than would be required if no liquid was employed.

My invention may be illustrated with reference to the accompanying drawing, in which Figures 1 and 2 represent diagrammatically apparatus in carrying out my invention.

Referring to Fig. l, (A) represents a gas-pro-v ducing well comprising a casing I provided with 2 sesame well being, for example, 4300 lbs/sq, 111., and at the well head, 3500 lbs/sq. in. The gas containing liquefiable hydrocarbons is withdrawn from the well head stv a. pressure of 3500 lbs/sq, in.

and is passed by means of valve-controlled pipe to a. suitable liquid hydrocarbon recovery apparatus 5, which may be an absorption tower opersting at a pressure oi, for example, 2500 lbs/sq. in. Dther conventionel apparatus for recovery of liquefisble hydrocarbons may be employed, such as a low pressure separator, or a low pres sure absorber, or a retrograde condensation system such as is shown'in U. S. Patent #2133344 to Vaughan. Since the liquenable hydocarbon recovery apparatus is exemplary only and forms no part of my invention, further detailed discussion thereof is unnecessary. Suifice to say that recovered liqueflable hydrocarbons, for example, of the nature of gasoline, are. withdrawn from the apparatus 5 through valve-controlled pipe 8 and disposed oi as desired. Gas stripped of llquefiable hydrocarbons is withdrawn from the apparatus 5 at a pressure of, for example, 2500 lbs/sq. in, and is returned to the gas-producing formation via input well as hereinafter described.

Input well (B) comprises a. casing I provided with perforations 8 communicating with the gas oroducing formation surrounding the bottom or said casing. Within the casing l is disposed a timing string 9 terminating above the perforated lower section of easing l. The annular space be-' tween casing. l and tubing 5 is blocked ofi edjacent the lower end of tubing 9 by means of a. pecker 30 provided with e. pipe ll terminating adjacent the bottom of the well. I

, Assuming the gas pressures in the top and bottom of input well (B) to be substantially the some as that existing in the top and bottom of the producmg well (A) i. e., 3500 lbs'./sq. in., and

vi300 lbs/sq. in. at 8000 feet, respectively, it would be necessary, under normal conditions, to introduce stripped gas into well (13) at a pressiu'e somewhat in excess of the wellhead pressure. for

example, 3600 lbs/sq. in., in order to return gas The difference in Vs to the producing formation. pressure between the top and bottom of the well is substantially accounted for by the weight of the columnof gas within the well, which may exert a. pressure of the order of 800 lbs/sq. in. in an 8,000 foot well.

In order to return stripped gas to input well ('3) at lower pump pressures than would ordinarily be required, I first introduce. a. liquid, for example, water, into tubing string 9 in such quantity as to fill the tubing 0, the bottom of the casing to a level indicated at 52, the pipe 5!, and the casing 7 above the pecker G0, the gas presll into tubing string 9 at a. pressure suillcient to overcome the gas pressure at the well head,

I i. e., 3500 lbs./ sq. in. The water is forced down the tubing string 8 and discharges into the bottom of the casing 1. When sufllcient water has collected in the bottom of the casing to submerge the lower end of pipe H, the gas pressure gas contained in the casing above the pecker Ill.

This gas may be vented from the top of easing 7 through valve-controlled pipe 38, gas separator 10 and valve-controlled pipe 20, valves ii and :22 being closed. when the casing I has been filled with water, and water appears in the separator IS, the supply of water from an extraneous source is shut off by closing valve ll,

and stripped gas, at a. pressure of, for example,

2500 lbs sq. in., is passed from hydrocarbon recovery apparatus 5 through valve-controlled pipe 23 to injector 16, valves 20 and 22 being closed and valve 2i being opened. The high pressure gas passing through injector i8 is introduced through pipe I! into the upper end of tubing string 9, thus forcing the water in the tubing string downwardly into the bottom of the well, whence it is.pas'sed by pipe ii to casing l, and thence upwardly through the casing to the casing head. The water is withdrawn from the casing head through valve-controlled pipe 18 and passed to gas separator i9, and is discharged therefrom by means of valve-controlled pipe 2|.

When the desired volume or water has been displaced from the tubing string 9, and removed at suitably elevated pressure, for example, 2500 lbs/sq. in., through pipe ii to injector it, wherein it is mixed with high pressure stripped gas from apparatus 5. The mixture 0! high pressure stripped gas and water is then continuously ted by the injector 90 through pipe i! into the top of tubing string 8, and is conducted downwardly through the tubing string in such a manner that the water exerts a, hydrostatic pressure upon the gas in the tubing sufficient to overcome. at least in part, the gas pressure existing at the bottom or the well. By proper regulation of the quantities of gas and water and the rate at which they are charged to the injector, the mixture of gas and water discharged from the injector may take sure at the bottom of the well being sufilcient to existing at the bottom of the casing forces the water upwardly through tubing section l! and casing 1 above the packer 30, thus displacing the the form of a. foam, or by periodically interrupting the flow of gas or water to the injector by means of valves 23 and 22 respectively, a. series of alternate slugs of gas and 0! water may be produced. Ineither case, the object is to introduce and conduct the gas and water down the tubing string 9 in such state that the water will exert a. hydrostatic pressure upon the gas as it flows through the tubing to the bottom of the well. The gas and water are discharged from the lower end of tubing string 0 into the tracing l below the packer E0, the water separating from the gas by dlfierence in gravity. The gas is passed from the casing by means of perforations B into the gas-producing formation surrounding the lower section of the well, and the separated water collecting in the bottom of casing I is continuously forced, by the well bottom gas pressure,

upwardly through pipe H into casing 1 above packer l0. and thence upwardly through the casing to the casing head, from which it is withdrawn at elevated pressure for recirculation to the'lnjector 55. In the event that the stripped g ns-mug,

for satisfactory operation of injector I, such gas may be passed from the apparatus 6 through valve-controlled pipe 24 to compressor 25, and thence delivered at higher pressure through pipes 26 and 23 to injector i6.

Assuming that the System is in continuousoperation and has reached an operating equilibrium in which the gas and the water each occupy half of the total, volume of tubing string 9, it will be apparent that in the 8,000 foot tubing string, the weight of the water will exert a pressure of about 1735 lbs/sq. in. and the weight of the gas will exert a pressure of about 345 lbs/sq. in., against a gas pressure of 4300 lbs./sq. in. at the bottom of the well. Therefore, the pressure required to continuously introduce gas and water, either as a. mixture, foam, or in slugs, into the top oi the tubing string will be of the order of 2220 lbs/sq. in. as against 3500 to 3600 lbs/sq. in. required if no water was employed in partially counter-balancing or overcoming the 4300 lbs/sq. in. well bottom pressure. And the water passing upwardly through casing l for recirculation to the injector 55, will exert a pressure of the order of 3470 lbs/sq. in. at the packer H), which is approximately 8000 feet below the earth's surface. Therefore the water issuing from the top of casing Z for recirculation will be under a pressure of about 830 lbs/sq. in.

From the description or my method above given, it will be apparent that once the gas return system is in operation, and the stripped gas is delivered to the return system at a sufficiently high pressure, the gas may be introduced into the well at substantially lower pressures than would be necessary if no liquid was employed to partially overcome the gas pressure existing in the well. While it is usually desirable to withdraw the liquid from the well, it is to be understood that such liquid may be passed from the casing, together with the gas, into the producing formation surrounding the well.

In Figure 2 of-the drawing is shown a modification of the input well (13) of Figure 1, wherein the gas and liquid are introduced into the top of casing l ll" and flow downwardly through the casing in I such a manner that the liquid exerts a hydroby means of valve-controlled pipe 4 and liquid downwardly through said well in such a manner that the liquid exerts a hydrostatic pressure upon the gassufllcient to overcome, at

least in part,- the gas pressure*existing'in said" well, separatlng said gas from said liquid adja-. cent the bottom of said well, passing said separated liquid upwardly and out of said well, and flowing said separated gas into the gas-producing formation surrounding said well.-

2. The method of returning gas to a high pressure gas-producing formation, which comprises introducing a mixture of gas and liquid into a well communicating with said formation, conducting said mixture downwardly through said well in such a manner that the liquid component of said mixture exerts a hydrostatic pressure upon the gas component thereof sufficient to over-- come, at least in part, the gas pressure existing in said well, separating said mixture into gas and liquid components adjacent the bottom of said Y well, passing said separated liquid component static pressure upon the gas. The gas and liquid pass through the short pipe ii provided in packer l0, and are separated adjacent the bottom of the well, the gas flowing through the perforations 8' into the gas-producing formation surrounding the bottom of the well, and the liquid collecting at I? being forced upwardly to the earths surface through tubing string 9' by the gas pressure existing at the bottom of the well. Liquid withdrawn from the upper end of tubing string 9' may be passed by means of pipe 58' to a gas separator and thence to a pump and an injector such as is shown in Figure 1, for recirculation to the well casing, along with gas to be returned to the well.

While my method of returning gas to a. gasproducing formation is designed primarily for use in conjunction with gas distillate wells, it is also applicable to the return of gas to oil-producing formations to repressure same or to maintain the gas pressure naturally existing in the oil-producing formation.

What I claim is:

1. The method of returning gas to a high pressure gas-producing formation, which comprises introducing'gas and liquid into a well communicating with said formation, conducting said gas upwardly and out of said well, and flowing said separated gas into the gas-producing formation surrounding said well. a

3. The method of returning gas to a high pressure gas-producing formation, which comprises alternately introducing gas and liquid into a well communicating with said formation, conducting said gas and liquid downwardly through said well in a succession of gas and liquid slugs, said liquid slugs exerting a hydrostatic pressure upon the gas sufilcient to overcome. at least in part, the gas pressure existing in said well, separating said gas from said liquid adjacent the bottom of said well, passing said separated liquid upwardly and out of said well, and flowing said separated gas into the gas-producing formation surrounding said well.

4. The method-of returning gas to a high pressure gas-producing formation through a well having a casing and a tubing string. terminating adjacent the bottom of said well, which comprises introducing a mixture of gas and liquid into said tubing string, causing said mixture to flow downwardly through said tubing and to discharge therefrom into said casing adjacent the bottom thereof, separating said liquid from the mixture so discharged, withdrawing said sepa-- rated liquid from said casing, and flowing said gas from said casing into the gas-producing formation surrounding said well.

5. The method of returning gas to a high pressure gas-produing formation through a. well having a casing and a tubing string terminating adjacent the bottom of said well, which comprises introducing a mixture of gas and liquid into said tubing string, causing said mixture to flow downwardly through said tubing in such a manner that the liquid component of said mixture exerts a hydrostatic pressure uponthe gas component thereof sufficient to overcome, at least in part, the gas pressure existing in said well, discharging said mixture from said tubing into said casing adjacent the bottom of said well, separating said liquid from the mixture so discharged. withdrawing said separated liquid from said casing, and flowing said gas from said easing into the gasproducing formation surrounding said well.

6. The method recited in claim 5, wherein the liquid employed is water.

7. The method of returning gas to a high pressure gas-producing formation. which comprises introducing adjacent the top of a well communicating with said formation, gas and liquid at a pressure substantially lower than that existing thereby forcing said gas downwardly through said well, separating said. gas from said liquid adjacent the mm c! said well. iorcing seid separated liquid upwardly and vout of said well by means of the gas pressure eflstmg at the bot-- tom 0! said well, and flowing said separated gas into the gas-producing formation -surrounding said-well. Y 

